Mkvmerge - FPS setting - can it change variable fps to constant?

[TheLastOfThem]

Kind of confused on this. Got a variable fps handbrake file...does setting the FPS to 1 number change it to constant fps??

[Selur]

You could use mkvmerge to change the frame rate flag of your file, but you would not change the content. Meaning you would just tell players to use a constant frame rate during playback and assuming a/v-playback was synchronous before it would be asynchronous.
You would need to reencode to do a vfr -> cfr conversion, which can't be done with mkvmerge.

[TheLastOfThem]

I'm sorry by asynchronous - do you mean OUT OF SYNC?

Because if so..I don't see that happening at all with my audio or the videos which are now a constant FPS....?

[Selur]

I'm sorry by asynchronous - do you mean OUT OF SYNC?

yes.

Because if so..I don't see that happening at all with my audio or the videos which are now a constant FPS....?

Don't see the question there. I just stated what mkvmerge is capable of and it can't do vfr to cfr conversions since those require reencoding.
-> My guess is that you remuxed a file, set a frame rate and dropped the time codes somewhere along the line and your source wasn't vfr to begin with.

[TheLastOfThem]

most definitely vfr with min and max fps. dropped time codes? not sure what u mean but why would that lead to a synced file?

[Selur]

If you speak of vfr and mkv and you don't know what time codes are you sure don't know what vfr means.
time codes = list of timings which indicate how long each individual frame should be shown
(cfr = all time codes have the same distance; vfr = the difference between time codes differs)
Sounds like mediainfo reported vfr and you assume it's always right. MediaInfo will report vfr if at least one for the first few time codes has a different distance to it's neighbors. So if one of the first few time codes is 'off' MediaInfo will report that the file is vfr.
-> look at the time codes of your file to check if you would call it vfr or not.

[TheLastOfThem]

You're right. Had no idea. Read up on it though!

I used Handbrake for .mkv files and it has a min/max FPS. Not sure how to check if the file is "VFR" in terms of its source. How can one check for that or KNOW if a show is VFR some scenes and CFR in others?

[Selur]

You would need to extract the time codes and look at those to be totally sure.
btw. if I remember correctly handbrake should have an option which tells it to produce cfr and not vfr output. (not totally sure since I don't use handbrake)
Normally no show is broadcasted as vfr.
Some webcam cameras and screencapturing tools produce vfr output and some folks use it for old animes, but normally there isn't much vfr content around unless folks decide to create it during reencoding.

[hello_hello]

I'm sorry by asynchronous - do you mean OUT OF SYNC?

Because if so..I don't see that happening at all with my audio or the videos which are now a constant FPS....?

It probably means they weren't really variable frame rate.
When you remux an mkv with MKVMergeGUI without specifying a frame rate, the output is the same as the source. When you specify a frame rate, it gives each frame the same duration. The number of frames doesn't change though, so generally remuxing VFR video while specifying a frame rate will change the total duration to some degree. Hence possible audio sync problems.
If you had Handbrake set for a CFR output, MediaInfo is probably getting it wrong. If you had it set to output VFR that might be a different story.

If you have ffdshow installed, it's on-screen-display can display timecodes and frame rates. That's probably the easiest way to do it. or Potplayer might have something similar built-in. If you extract the timecodes (gMKVExtractGUI will do it) you get a large text file containing lots of numbers that would take a lot of time to check.

The frame durations are generally to the nearest millisecond, so for a 23.976fps video it'll alternate between 41ms and 42ms frame durations. That's normal.